Disk drives, also called disk files, are information storage devices that use a rotatable disk with concentric data tracks containing the information, a head or transducer for reading and/or writing data onto the various tracks and an actuator connected to a carrier for the head for moving the head to the desired track and maintaining it over the track centerline during read or write operations. There are typically a plurality of disks separated by spacer rings and stacked on a hub that is rotated by a disk drive motor. A housing supports the drive motor and head actuator and surrounds the head and disk to provide a substantially sealed environment for the head-disk interface.
In conventional magnetic recording disk drives, the head carrier is an air-bearing slider that rides on a bearing of air above tile disk surface when the disk is rotating at its operational speed. The slider is maintained next to the disk surface by a relatively fragile suspension that connects the slider to the actuator. The slider is either biased toward the disk surface by a small spring force from the suspension, or is "self-loaded" to the disk surface by means of a "negative-pressure" air-bearing surface on the slider.
To improve the wear resistance of the disk, as well as to maintain consistent magnetic properties, it is desirable to make the disk surface as smooth as possible. However, a very smooth disk surface creates a problem known as "stiction". This means that after the slider has been in stationary contact with the disk for a period of time, the slider tends to resist translational movement or "stick" to the disk surface. Stiction is caused by a variety of factors, including static friction and adhesion forces between the disk and slider created by the lubricant on the disk. Stiction in a disk drive can result in damage to the head or disk when the slider suddenly breaks free from the disk surface when disk rotation is initiated. In addition, because the suspension between the actuator and the slider is relatively fragile in order to permit the slider to fly above the disk surface, sudden rotation of the disk can also damage the suspension. In some disk drives, such as low-power disk drives used in laptop and notebook computers, the drive motor may simply be unable to initiate rotation or achieve operating speed because of the adhesion forces that cause stuck sliders or excessive drag.
Contact start/stop (CSS) disk drives operate with the slider in contact with the disk surface during start and stop operations when there is insufficient disk rotational speed to maintain the air bearing. To minimize the effect of stiction, CSS disk drives often use a dedicated "landing zone" where the slider is parked when the drive is not operating. Typically, the landing zone is a specially textured nondata region of the disk. In contrast to CSS disk drives, "load/unload" disk drives address the stiction problem by mechanically unloading the slider from the disk when the power is turned off, and then loading the slider back to the disk when the disk has reached a speed sufficient to generate the air bearing. The loading and unloading is typically done by means of a ramp which contacts the suspension when the actuator is moved away from the data region of the disk. The slider is thus parked off the disk surface with the suspension supported in a recess of the ramp.
However, both CSS disk drives with landing zones and load/unload disk drives have inherent failure mechanisms that can result in the slider coming to rest on the disk. For example, external shocks can displace the slider from the landing zone or the load/unload ramp, and errors in the microcode controlling the actuator can inadvertently cause the slider to land on the disk.
The above description of the stiction problem and the operation of CSS and load/unload disk drives is not limited to the conventional air-bearing type of disk drive, but also applies to the liquid-bearing type of disk drive. In one type of liquid-bearing disk drive, as described in IBM's pending application, U.S. Ser. No. 264,604, filed Oct. 31, 1988, and published May 9, 1990, as European published application EP 367510, and in U.S. Pat. No. 5,097,368 assigned to Conner Peripherals, a relatively thick, continuously recirculating liquid film is maintained on the disk surface and the head carrier is maintained in continuous contact with the liquid film when the disk is rotating at its normal operating speed. In a variation of the liquid-bearing disk drive, as described in U.S. Pat. No. 4,901,185 assigned to Toshiba and U.S. Pat. No. 5,202,803 assigned to IBM, a combined air and liquid bearing supports the head carrier, which is in contact or partial contact with a relatively thin liquid film on the disk.
Thus, in both air-bearing and liquid-bearing disk drives, it is desirable to find a means for freeing the head carriers from the disks to which they are stuck, and for returning the carriers to their preferred parking location, i.e., the landing zone or load/unload ramp, when the stiction has been removed.